1. Field of the Invention
The present invention relates to an optical scanning apparatus to be provided in an image forming apparatus using an electrophotography technique and an image forming apparatus provided with the same.
2. Description of the Related Art
Conventionally, an image forming apparatus using the electrophotographic process scans a surface of a photosensitive member which is charged with a light beam emitted from a light source based on image data and forms a latent image on the photosensitive member. The formed latent image is developed by developer, and the developed toner image is transferred and fixed onto paper. An optical scanning apparatus that scans the light beam includes a rotating polygon mirror (i.e., polygon mirror).
In recent years, image forming apparatuses capable of forming images with a high image quality have been demanded. One of the factors that hinder formation of the images with high image quality is dirt over time on the reflection surfaces of the polygon mirror. When the polygon mirror is rotated at a high speed, an atmospheric pressure around the polygon mirror is lowered inside the optical scanning apparatus. Air containing minute dust that exists within the optical scanning apparatus flows into a space where the atmospheric pressure has been lowered. The dust hits and adheres onto the reflection surfaces of the polygon mirror. When the dust adheres to the reflection surfaces, light reflectance of the mirror is lowered. As a result, a light quantity of the light beam that reaches the photosensitive member is reduced than a desired light quantity, which affects the image density, and eventually causes image deterioration.
Japanese Patent Application Laid-Open No. 6-148550 discusses a configuration in which a transparent member for protecting the reflection surfaces of the polygon mirror from the dust is removably attached to the polygon mirror. The transparent member can suppress adhesion of the dust to the reflection surfaces of the polygon mirror.
A dustproof cover is attached to an optical box of the optical scanning apparatus discussed in Japanese Patent Application Laid-Open No 6-148550, and the dustproof cover is provided with an open-close lid. When the dust adheres to the transparent member, a service staff opens the open-close lid on site and replaces the transparent member. Since the dustproof cover is provided with the open-close lid, the transparent member can be changed without removing the dustproof cover, accumulation of the dust on a lens, a mirror, or the like can be prevented, even if the transparent member is changed on site.
When the transparent member discussed in Japanese Patent Application Laid-Open No. 6-148550 is attached to the polygon mirror, a drive motor which can produce a torque by which both the polygon mirror and the transparent member can be rotated is required, and thus manufacturing cost of the optical scanning apparatus will increase. Further, the manufacturing cost of the optical scanning apparatus increases since the transparent member is necessary. Accordingly, a configuration such as attaching the transparent member to the polygon mirror has not been employed in recent years, and the service staff wipes the dirt off the reflection surfaces of the polygon mirror on site during a periodic maintenance. By the cleaning work by the service staff, degradation of the image quality of output images due to the contamination of the reflection surfaces of the polygon mirror can be suppressed.
However, when the service staff opens the open-close lid and performs cleaning work for wiping the dirt off the reflection surfaces of the polygon mirror, edges of opening of lid member, side walls of the optical box, and optical members such as lens can disturb the cleaning work.